European Patent document no. 473 258 A2 refers to an intake valve that is opened twice during one working period. The first opening begins in the range of the top dead center of a piston and ends in the intake stroke during the downward movement of the piston.
The second opening begins at or after the lower dead center of the piston, at the beginning of the compression stroke, and ends before the end of the compression stroke. The exemplary method is used at low loads of the internal combustion engine, which are distinguished by a low charge of the combustion chamber with combustible mixture. This slight quantity may be sucked in already using a relatively short first opening of the intake valve. Therefore, the intake valve may be closed before the end of the intake stroke.
Because of the piston running further in the direction of the bottom dead center while the intake valve is closed, a decreasing pressure is generated in the combustion chamber, whose absolute value undershoots the intake manifold pressure. Because of this pressure drop, upon the second opening of the intake valve in the bottom dead center or after the bottom dead center, additional air or additional mixture flows into the combustion chamber. The flow brought on by the pressure drop causes a desired turbulence in the combustion chamber, which improves the preparation of the mixture for the subsequent combustion.
To the extent that this involves the heating of a catalytic converter in the exhaust gas of the internal combustion engine, this document suggests an earlier opening of the exhaust valve in the combustion stroke, because in this way less energy would be converted to mechanical work, and as a result, the exhaust gases would be hotter. In order to heat up a catalytic converter and to reduce hydrocarbon emissions after a cold start of an internal combustion engine, frequently so-called secondary air is blown in after the exhaust valves of the internal combustion engine. The secondary air is blown in as fresh air via an electric pump, and it allows for the oxidation of uncombusted hydrocarbons in the exhaust gas that is still hot.
In this context, the internal combustion engine may be operated using excess fuel, so as to supply hydrocarbons as reaction partner for the secondary air blown in. The post-oxidation of the hydrocarbons not combusted in the combustion chamber using the blown-in secondary air generates an exothermic reaction in the exhaust gas system and allows for a rapid heating up of the catalytic converter.
In this context, one may differentiate between a reaction in the exhaust manifold and a reaction in the catalytic converter. If a reaction is desired in the manifold, the exhaust gas has to come together with the secondary air as early as possible after the combustion of the combustion chamber charge. Therefore, the location of introduction of the secondary air often lies directly at the exhaust valves of the internal combustion engine.
Besides the classical injection of secondary air with the aid of an electric pump, one may operate individual cylinders of an internal combustion engine alternatingly using excess fuel and excess oxygen, in order to achieve a secondary air effect upon guiding together the exhaust gas from the combustion with excess fuel with the exhaust gas from the combustion with excess air.